The present invention relates to a coil unit relating to non-contact power transmission using a coil, a method of manufacturing the same, an electronic instrument, and the like.
Non-contact power transmission has been known which enables power transmission without metal-to-metal contact utilizing electromagnetic induction. As application examples of non-contact power transmission, charging a portable telephone, a household appliance (e.g., telephone handset), and the like has been proposed.
In recent years, a reduction in size of portable telephones has been increasingly desired. This makes it necessary to reduce the size (particularly thickness) of a power transmission coil unit. JP-A-8-148360, JP-A-2005-26743, and JP-A-2005-260122 disclose technologies relating to a reduction in size of a coil unit.
JP-A-8-148360 discloses technology in which the thickness of a coil of a non-contact power transmission module is reduced using a soft magnetic sheet instead of ferrite. This technology is useful for reducing the thickness of a magnetic material. On the other hand, the thickness of the remaining portion of the coil unit cannot be reduced to a large extent using this technology.
JP-A-2005-26743 discloses technology which reduces the thickness of a coil unit by employing a structure which is affected to only a small extent by a surrounding metal under a use environment of a non-contact IC card. Specifically, a non-contact IC card is stably written/read without being affected by a surrounding metal by disposing two metal sheets on the back side of an antenna and a magnetic material and tuning the antenna. However, the metal sheet produces heat when applying this technology to non-contact power transmission. Moreover, since it is necessary to tune each antenna, mass productivity deteriorates due to an increase in cost.
JP-A-2005-260122 discloses technology which reduces the size of a non-contact power transmission module by forming the non-contact power transmission module using a flexible printed circuit (FPC) board. JP-A-2005-260112 discloses technology in which a coil section and a circuit section are formed so that a flexible printed circuit board can be folded at an intermediate point between the coil section and the circuit section, and the flexible printed circuit board is mounted by folding the flexible printed circuit board to sandwich a pot-type core. This technology is useful when using a ferrite material as the material for the core. However, the coil placement shape cannot be formed when using a sheet-shaped magnetic material. Moreover, it is difficult to apply this technology when using a wound coil and a substrate.